Page 62 - ICSE Chemistry 6

Property Solids Liquids Gases

Compressibility Solids are almost incom- Liquids can be compressed to Gases can be compressed
pressible. some extent. easily.

Diffusion Solids do not diffuse. Liquids diffuse slowly. Gases diffuse quickly.
Density Solids have high density. Liquids have low density. Gases have very low density.

EXPLANATION FOR THE EXISTENCE OF THREE STATES OF MATTER

Solids

The molecules are closely packed in solids. The force of a rac on between the molecules is very strong
and the space between them is very small. As a result, the molecules are not able to move freely. They
vibrate about their mean posi ons. It is due to this reason that solids are hard and incompressible, and
thus have a defi nite shape and size.

Liquids

The molecules are not very closely packed in liquids. They do not have strong intermolecular forces of
a rac on. As a result, the intermolecular spaces are compara vely larger, that allow the molecules to
move freely. This makes the liquid fl ow and take the shape of the container into which it is poured. Thus,
liquids have a defi nite volume but no defi nite shape.
Gases

The molecules lie far apart from each other and hardly a ract each other in gases. Therefore, the
intermolecular spaces are very large. The molecules move rapidly as the intermolecular force of a rac on
is very weak. As a result, gases neither have a defi nite shape nor a fi xed volume. The gases can be
compressed easily.

Reasons for Differences in Properties of Three States of Matter

The diff erence in proper es of states of ma er is due to the following factors.
• Intermolecular space • Cohesive forces or intermolecular forces
• Random mo on of par cles

Intermolecular Space

Intermolecular space is the space between the par cles of ma er. This space is almost negligible in solids.

Cohesive Forces or Intermolecular Forces

Cohesive forces are the intermolecular forces (a rac ve Know Your Scientist
forces) that exist between molecules of the same
Robert Brown, a Sco sh botanist discovered
substance. The cohesive forces in solids are strong. Some the random movement of par cles. Thus, this
liquids such as mercury also possess strong cohesive mo on of par cles is known as the Brownian
forces. mo on.
Random Motion of Particles

The random mo on of par cles induces diff usion and Brownian mo on.

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